Thermographic apparatus

ABSTRACT

Thermographic apparatus comprising a trough for thermographic powder, feeding means to feed a workpiece bearing freshly printed matter into the trough, withdrawal means to withdraw from the trough the workpiece with thermographic powder adhering to said freshly printed matter, and vibrator means to vibrate the workpiece free of surplus powder as it leaves the trough. Electrical heating means for heating the freshly printed workpiece (having thermographic powder adhering to the printed matter) as the workpiece moves relative to the heating means comprises a plurality of separately energisable elongate heating elements directed longitudinally of the path of said relative movement.

United States Patent [1 1 Ayers 1 1 THERMOGRAPHIC APPARATUS [76] Inventor: Ronald Frederick Ayers, 15-19 Church St., Twickenham, Middlesex, England [22] Filed: Sept. 13, 1974 [21] Appl. No.: 506,188

Related US. Application Data [63] Continuation of Ser. No. 288,939, Septv 14, 1972,

abandoned.

[52] US. Cl 118/68; 118/405 [51] Int. Cl. BOSC 3/02; G03G 13/08 [58] Field of Search 1 18/404, 405, 413-415,

118/57, 58, 642, 68; 117/1 15; 219/266, 388; 95/89 A; 355/3 DD [56] References Cited UNITED STATES PATENTS 1,149,455 8/1915 Lipsius 118/57 1,867,405 7/1932 Gurwickm. 101/211 UX 2,357,851 9/1944 Scheyer 117/115 X 2,674,809 4/1954 Meinhofer 118/642 X 3,013,891 12/1961 Block 118/57 X Aug. 19, 1975 3,021,817 2/1967 Limberger 118/637 3,342,160 9/1967 Weeks 118/126 X 3,629,555 12/1971 Herbert, Jr. 219/388 X Primary Examiner-Morris Kaplan Attorney, Agent, or Firm-Groff & Groff [57] ABSTRACT Thermographic apparatus comprising a trough for thermographic powder, feeding means to feed a workpiece bearing freshly printed matter into the trough, withdrawal means to withdraw from the trough the workpiece with thermographic powder adhering to said freshly printed matter, and vibrator means to vibrate the workpiece free of surplus powder as it leaves the trough.

Electrical heating means for heating the freshly printed workpiece (having thermographic powder adhering to the printed matter) as the workpiece moves relative to the heating means comprises a plurality of separately energisable elongate heating elements directed longitudinally of the path of said relative movement.

9 Claims, 3 Drawing Figures PATENTE AUG-1 9197s SHEET 1 BF 2 THERMOGRAPl-IIC APPARATUS This is a continuation of application Ser. No. 288,939, filed Sept. 14, l972, now abandoned.

BACKGROUND OF THE INVENTION This invention relates to thermographic apparatus, i.e. to apparatus for use in the known printing process termed thermography. In this process, a thermographic powder is applied to a workpiece of printed matter while the printing ink is still wet or tacky on the work piece so that the powder will adhere to the print, the workpiece is then treated, generally by suction, to rid the unprinted parts of the workpiece of surplus powder, and the workpiece is then passed beneath a heater which acts on the powder adhering to the ink. Thermographic powder is one having the property of fusing, and preferably to some extent swelling, under heat treatment, and then drying off into a glossy mass preferably giving a somewhat high relief to the printed matter. For example the thermographic powder may be a resinous composition. Metallic thermographic powders are also known and available containing metallic particles.

SUMMARY OF THE INVENTION The object of the present invention is to provide apparatus for expeditiously and economically applying the thermographic powder to a workpiece of printed matter, and/or to introduce heat where appropriate.

According to one aspect of said invention there is provided thermographic apparatus comprising a trough for thermographic powder, feeding means to feed a workpiece bearing freshly printed matter into the trough, withdrawal means to withdraw from the trough the workpiece with thermographic powder adhering to said freshly printed matter, and vibrator means to vibrate the workpiece free of surplus powder as it leaves the trough.

According to another aspect of said invention there is provided thermographic apparatus with heating means for heating a freshly printed workpiece, that has thermographic powder adhering to the print, as said workpiece and heating means move relative to one another, the said heating means comprising a plurality of separately energisable elongate heating elements directed longitudinally of the path of said relative movement.

BRIEF DESCRIPTION OF THE DRAWINGS By way of example, one embodiment of the invention will now be described with reference to the accompanying drawings of which:

FIG. 1 is a longitudinal cross-section of thermographic apparatus according to the invention;

FIG. 2 is a cross-sectional view taken along the line II-II of FIG. 1; and

FIG. 3 is a cross-sectional view along the line III-III of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a preferred embodiment of the invention, the apparatus comprises a somewhat v-shaped trough containing a resinous thermographic powder, co-operating feed rollers to feed into the grough a paper or card workpiece bearing freshly printed matter (e.g. letter headings) to be thermographically treated, co-

operating take-up rollers to withdraw the workpiece (with thermographic powder adhering to printed matter) from the trough, and a solenoid operable vibrator blade or fail for striking the workpiece and to shake off non-adhering, unwanted surplus powder from portions of the workpiece that have passed through the thermographic powder.

Heating means are provided to apply heat to a freshly printed workpiece, having thermographic powder adhering to the print, during relative motion between said heating means and said workpiece. The heating means may have a plurality of elongate electric heating elements which are individually encapsulated and separated by reflectors. These elongate elements are preferably directed parallel to one another longitudinally of the relative motion direction, and arranged to be individually energisable.

More particularly such a preferred embodiment has the following construction: A feed platform is inclined to the horizontal so as to deliver sheet like workpieces downwardly by gravity or with suitable power assistance, and at the exit end of the platform there is provided a pair of transfer rollers. The latter form a nip between their peripheries, one being driven, to take up the end of a workpiece and push it through to a powder trough in the form of a gentle concave curve bending upwards to a delivery pathway lying advantageously at least 55 and preferably at least to the horizontal and extending outwards from the powder trough.

The said delivery pathway terminates at its upper end in a suitable vibrator device which may be electrically, electromagnetically or mechanically operated. By this means the workpieces are rid of powder which is in excess to that required by the actual printed areas. At or near the positioning of the vibrator, there is disposed a pair of reception rollers which grip the workpieces and, besides assisting the lifting process up the delivery pathway, serve to transfer the workpieces to a conveyor which carries them along to a heater for fusing the powder present on the workpiece.

Although the workpiece will usually follow closely the configuration of the trough and delivery pathway, there is found, in exceptional circumstances, a tendency for the workpiece to miss the trough and form a chord across the arc thereof, thus missing the powdering stage. This tendency may be eliminated by the provision of an idler guide-roller placed deep within the angle subtended by the trough and delivery pathway, which assists in keeping the curvature on the workpiece.

The distance between the two pairs of rollers (measured along the path taken by the workpiece) must be less than the length of the workpiece so that at least one pair of rollers always has control of the paper. It is to be understood that various roller arrangements may be employed.

The heater, when employed, may have an area of separate heating elements of which all, one, or some may be selectively brought into action. Preferably, the conveyor belt carrying the workpiece passes through a heat-insulated tunnel. The heating elements are fitted within the ceiling of said tunnel in a manner to lie flush therewith, preferably being encapsulated in ceramic blocks, although metal blocks may be employed. Such encapsulation permits a substantially constant level of heat over the whole ceiling surface, when all the elements are in operation. However, it is very desirable to be able to employ only one or more heating elements, with some workpieces which may be printed over only a small part of their surface.

Such part-use of heating has obvious benefits in terms of power economy and waste heat production.

Therefore it is hereby proposed to dispose the heating elements to lie with their long axes parallel to the direction of flow of the workpieces and to be capable of use either singly or in any combination of elements. In order to obtain maximum benefit from each element, it is preferred to position at least one reflector between each pair of elements, so disposed as to project downwards from a position midway between each pair of elements and parallel and co-terminous to the longitudinal axis thereof, and projecting at rightangles to the ceiling-surface of the heating tunnel. The reflectors are provided with a reflective surface on both sides, and are preferably made of stainless steel.

The apparatus embodying the invention and shown in FIG. 1, comprises two stages: a print powdering stage leading to heating stage 12. The print powdering stage 10 has a feed station 14 at which freshly printed paper (or card) workpieces to be subjected to thermography are fed. From the feed station 14, a stainless steel feed tray 15 for the workpieces extends downwardly to the nip or pinch formed between a pair of coaxial rubber-sleeved feed rollers 16 (only one roller being visible in FIG. 1) and a mild steel shaft or roller 17 extending the width of the apparatus. The two coaxial rollers 16 are movable laterally of the apparatus so as to be adjustable in position so that they do not contact freshly printed matter on the workpieces (which for example may be letter headings). In use, the lower roller or shaft 17 is driven and the upper pair of rollers 16 are allowed to idle, although if desired they too can be driven. The downwardly inclined feed tray 15 has two side cheeks 18 which are movable laterally of the apparatus along a transverse bar 19 so as to be adjustable to the dimensions of the freshly printed fed workpieces. The side cheeks 19 can be manually clamped in their adjusted positions by screw-threaded devices 20.

Beyond the feed rollers 16, 17 the path (indicated by arrows 21) of the workpieces is defined by the stainless steel tray 23 containing thermographic powder 11. As shown, the inlet portion 24 of the base 22 is flattened somewhat to prevent the leading edge of the card or paper workpieces leaving the feed rollers 16, 17 from being stopped by the edge of the inlet portion 24. An upstanding baffle plate 25 extending between fixed, sectorially-shaped side cheeks 26 of the powder tray 23, descends to within a small distance of the tray base 22. The fixed gap 27 so formed between base 22 and baffle plate 25 is large enough to allow the passage therethrough of the thickest paper or card it is envisaged will be fed to the apparatus, yet is small enough to restrict to a minimum accidental leakage or ejection of thermographic powder contained in tray 23. Preferably the height of this gap is between 0.01 and 0.1 inch (25 um and 2.5 mm). It will be seen from FIG. 1 that in general terms the nip or pinch between rollers 16, 17 lies on the same arc of a circle as the powder-tray base 22, and that the feed tray 15 extends along a tangent to said arc at that point. The shape of the trough formed by the powder tray 23 and the baffle plate 25 is generally like that of the Greek letter 11. The inclination of tray 15 is sufficiently steep to enable cards or paper sheets to slide down it under gravity.

An aluminium idler roller 28 extends between the side-cheeks 26 of powder tray 23 above the powder tray base 22 in the vicinity of its lowermost point and rests upon the mass of powder 11. The idler roller 28 is free to move bodily up the powder tray 23 and rotate in the direction shown. In conjunction with the baffle plate 25, the idler roller 28 retains the thermographic powder substantially localised in the one region indicated by the mass of powder 11.

The powder tray 23 curves upwardly towards the nip or pinch formed between a pair of co-axial rubbersleeved withdrawal rollers 29 (only one roller 29 being visible in FIG. 1) and a mild steel shaft or roller 30 extending the width of the apparatus. In use the shaft or roller 30 is driven and the pair of co-axial rollers 29 are allowed to idle, although if desired they too can be driven. The co-axial rollers 29 are movable laterally of the apparatus so as to enable them to be positionally adjusted for their non-engagement of the thermographic powder adhering to the freshly printed matter. Between the uppermost extremity of the powder tray base 22 and the nip or pinch of rollers 29 and 30, there is disposed the leading tip 31 of an upwardly curved end portion of a blade 32. The other end of the blade 32 is connected via a block 33 of magnetisable material and a leaf spring 34 to a support 35 for an electromagnetically actuable armature 30 cooperable with the block 33. The electromagnet has its coil connected in series with a variable resistance and is adapted to be driven from the mains electricity supply. Thus the frequency of the vibrations executed by the blade 32 will correspond to the mains frequency of 50 or Hz, and the vibration amplitude will be controllable by the series-connected variable resistance, preferably to between about O.l and 0.15 inch (2.5 and 3.8 mm). The amplitude of the vibrations can also be altered by adjusting the air gap between the armature 36 and block 33 or the effective length of the leaf spring 34. The support 35 has a large mass to minimise transference of the vibrations to the remainder of the apparatus.

A removable stainless-steel bar 37 extending the width of the apparatus acts as a support for paper workpieces leaving the withdrawal rollers 29 and 30, which workpieces are not supported along their entire width by the rollers 29, 30. The bar 37 thus aids in controlling the attitude of the paper entering as well as leaving the rollers 29, 30 so that the vibrator blade tip 31 can strike the paper consistently from its leading edge to its trailing edge. Small, relatively stiff workpieces (e.g. card) do not require such support and the bar 37 is therefore removable.

If desired, an under-tray 38 may be provided beneath the trays 15, 23 and the shaft or roller 30 to catch any spilt thermographic powder. The under tray 38 is provided with side-cheeks 39 and with an appropriately dimensioned cut-out for the extension therethrough of the vibrator blade 32.

In use of the apparatus, freshly-printed paper or card workpieces (of a size in the direction of movement at least equal to the distance between the feed rollers 16, l7 and the withdrawal rollers 29, 30 measured around the powder tray periphery) are individually and sequentially fed, preferably manually, to the apparatus at the feed station 14. As each workpiece descends the incline of feed tray 15 under gravity, its leading edge enters feed rollers 16, 17 which feed the workpiece through the gap 27 and into the mass 11 of thermographic powder. The powder adheres to the wet or tacky printed matter on the workpiece which then passes on between the idler roller 28 and the base 22 of the powder-tray 23. The leading edge of the workpiece is guided upwardly by the powder tray base 22 until it passes the tip 31 of the vibrator blade 32. Obstruction of the workpieces leading edge by the blade 32 is avoided by reason of the upward curvature of the blades end portion. The vibrations imparted by the vibrator blade 32 to the workpiece portions downstream of the idler roller 28 to shake off surplus powder are damped out by the idler roller 28 and are substantially not imparted to the workpiece portions upstream of the idler roller 28 and in the mass 11 of thermographic powder. The latter is thus substantially undisturbed by the vibrations. The workpiece is ejected from the printpowdering stage by the withdrawal rollers 29, 30 to pass over the support bar 37 (if present) and on to the upper surface of a mesh-link conveyor belt 40 of the drying stage 12.

The mesh link conveyor belt 40 extends between a drive roller 41 and an idler roller 42. The rollers 41, 42 are rotatable, in the directions shown, by a variable speed motor to have a peripheral speed comparable to the peripheral speed of the rollers 29, 30. Thus the paper or card transfer speed is approximately the same in both stages 10 and 12. The upper surface of the conveyor belt 40 passes through an electrical heater 43. As best shown in FIGS. 2 and 3, the heater 43 comprises a thermally insulated parallelepiped housing 44, the lower surface of which passes beneath the conveyor belt 40. Five long encapsulated electric heating elements 45 are supported from the upper surface of housing 44 and are separated from one another by polished stainless-steel plates 46 acting as reflectors. The plates 46 extend downwards to within approximately 0.25 inch (6 mm) of the conveyor belt 40, as do end reflector plates 47 which help to trap hot air within the housing. The encapsulated heating elements 45 extend parallel to one another in the direction 21 of conveyor belt and workpiece motion. Each of the elements 45 is individually energisable by switch means (not shown) connected separately to opposite terminals 48 of each heating element 45. Thus heat may be continuously applied locally only to selected sections of the travelling workpiece. In use the sections selected for heat treatment will be those areas of the workpiece which have been printed and have thermographic powder adhering to the print. As the paper or card workpiece passes through the heater, the thermographic powder is fused and somewhat swelled to dry off into a glossy, raised mass conforming in outline to the matter printed on the workpiece fed to the apparatus.

It will be appreciated that as many parts as possible of the above described apparatus, particularly the print-powdering stage 10, are of metal to avoid an undue build-up of static electricity affecting the thermographic powders adhesion fully, but only, to the pre-printed matter. The apparatus is preferably grounded or earthed in use.

It will be understood that the above description of the present invention is susceptible to various modification changes and adaptations.

What is claimed is:

l. Thermographic apparatus for the application of thermographic powder to a workpiece bearing freshlyprinted matter, comprising: a trough of generally V -shaped transverse cross-section for said thermographic powder, the transverse powder retaining walls of said trough being defined by an upwardly concave, workpiece support surface and a plate extending up wardly from a lower region of said upwardly concave surface, and the upper transverse extremities of the troughs transverse powder-retaining walls being defined by the upper transverse edges of said plate and surface; feeding means to feed a workpiece bearing freshly-printed matter into the trough between the lower transverse edge of said plate and said lower surface region and along at least part of said workpiece support surface; withdrawal means to withdraw the workpiece with thermographic powder adhering to said freshly-printed matter from the trough along at least part of said workpiece support surface and past the latters upper transverse edge defining one of said upper transverse extremities of the trough; a floating roller disposed within said trough in the region of said workpiece infeed and beneath which the workpiece passes; and vibrator means to vibrate the workpiece free of surplus powder as it leaves the trough.

2. Thermographic apparatus comprising an upwardly concave, workpiece support surface and a plate extending upwardly from a lower region of said upwardly concave surface, said surface and plate defining transverse powder-retaining walls of a trough of generally V -shaped transverse cross-section to contain thermographic powder substantially in one region above a base portion of the trough, the upper transverse extremities of said troughs transverse powder-retaining walls being defined by the upper transverse edges of said plate and surface, means defining an entrance to the trough at least adjacent the bottom thereof and said lower surface region, feeding means to feed a workpiece bearing freshly-printed matter through said entrance into the trough and along at least part of said workpiece support surface, an idler roller resting on said surface and beneath which the workpiece is to pass, withdrawal means to withdraw the workpiece with thermographic powder adhering to said freshly printed matter from said trough along at least part of said workpiece support surface and past the latters upper transverse edge defining one of said upper transverse extremities of the trough, and vibrator means to vibrate the workpiece free of surplus powder as it leaves the trough.

3. Apparatus according to claim 2, wherein the entrance defining means comprises the lower transverse edge of said plate and means mounting said plate with said lower edge thereof spaced by a set distance above said lower region of the upwardly concave surface.

4. Apparatus according to claim 2, wherein the feeding means and withdrawal means each comprise a plu rality of first co-axial rollers, at least one second roller associated with the first rollers, and means mounting said first rollers for rotation in cooperation with the associated second rollers and for axial movement to avoid contact with said freshly-printed matter.

5. Apparatus according to claim 1, further comprising means downstream of said withdrawal means and defining an exit path for the workpiece with adherent thermographic powder, and heater means in said exit path having a plurality of individually energizable heating elements transversely spaced across said exit path and each directed longitudinally of said exit path.

6. For the application of thermographic powder to a flexible planar article bearing freshly-printed matter, thermographic apparatus comprising a receptacle to contain thermographic powder, and means to move a said article along a path transversely of said receptacle and through thermographic powder therein, wherein said receptacle has a cross-section in said path of movement that is generally 1/ -shaped and provided by first and second receptacle walls that extend upwardly away from the receptacle bottom and from a line of nearest mutual approach of said first and second receptacle walls, which line is at least adjacent said receptacle bottom, said walls forming an entrance slot at said line of nearest mutual approach, said second receptacle wall being concave with its upper surface providing, throughout its length, a support surface for a said article moving sequentially through the slot and through the receptacle, said first and second receptacle walls being mounted to extend away from one another as they extend upwardly away from said line of nearest approach, and an idler roll contained in the receptacle and resting on said surface and beneath which the article passes.

7. Thermographic apparatus according to claim 6 comprising take-up means to move the workpiece with thermographic powder adhering thereto from the trough along a path, and heater means in said path having a plurality of individually energizable elongate heating elements spaced from one another transversely of said path and each directed longitudinally of said path.

8. Apparatus according to claim 7, wherein said elongate heating elements are electrically energizable and are disposed parallel to one another substantially equi spaced from one another transversely of said path.

9. Apparatus according to claim 6 comprising a preentrance support for a said article; and wherein said entrance slot is defined by the lower edge of said first receptacle wall and the upper surface of said second receptacle wall, and said second receptacle wall projects past said entrance and externally of the receptacle to form said pre-entrance support and a restraint against loss of any powder leaking through said entrance. 

1. Thermographic apparatus for the application of thermographic powder to a workpiece bearing freshly-printed matter, comprising: a trough of generally Nu -shaped transverse cross-section for said thermographic powder, the transverse powder retaining walls of said trough being defined by an upwardly concave, workpiece support surface and a plate extending upwardly from a lower region of said upwardly concave surface, and the upper transverse extremities of the trough''s transverse powder-retaining walls being defined by the upper transverse edges of said plate and surface; feeding means to feed a workpiece bearing freshlyprinted matter into the trough between the lower transverse edge of said plate and said lower surface region and along at least part of said workpiece support surface; withdrawal means to withdraw the workpiece with thermographic powder adhering to said freshly-printed matter from the trough along at least part of said workpiece support surface and past the latter''s upper transverse edge defining one of said upper transverse extremities of the trough; a floating roller disposed within said trough in the region of said workpiece infeed and beneath which the workpiece passes; and vibrator means to vibrate the workpiece free of surplus powder as it leaves the trough.
 2. Thermographic apparatus comprising an upwardly concave, workpiece support surface and a plate extending upwardly from a lower region of said upwardly concave surface, said surface and plate defining transverse powder-retaining walls of a trough of generally Nu -shaped transverse cross-section to contain thermographic powder substantiAlly in one region above a base portion of the trough, the upper transverse extremities of said trough''s transverse powder-retaining walls being defined by the upper transverse edges of said plate and surface, means defining an entrance to the trough at least adjacent the bottom thereof and said lower surface region, feeding means to feed a workpiece bearing freshly-printed matter through said entrance into the trough and along at least part of said workpiece support surface, an idler roller resting on said surface and beneath which the workpiece is to pass, withdrawal means to withdraw the workpiece with thermographic powder adhering to said freshly printed matter from said trough along at least part of said workpiece support surface and past the latter''s upper transverse edge defining one of said upper transverse extremities of the trough, and vibrator means to vibrate the workpiece free of surplus powder as it leaves the trough.
 3. Apparatus according to claim 2, wherein the entrance defining means comprises the lower transverse edge of said plate and means mounting said plate with said lower edge thereof spaced by a set distance above said lower region of the upwardly concave surface.
 4. Apparatus according to claim 2, wherein the feeding means and withdrawal means each comprise a plurality of first co-axial rollers, at least one second roller associated with the first rollers, and means mounting said first rollers for rotation in cooperation with the associated second rollers and for axial movement to avoid contact with said freshly-printed matter.
 5. Apparatus according to claim 1, further comprising means downstream of said withdrawal means and defining an exit path for the workpiece with adherent thermographic powder, and heater means in said exit path having a plurality of individually energizable heating elements transversely spaced across said exit path and each directed longitudinally of said exit path.
 6. For the application of thermographic powder to a flexible planar article bearing freshly-printed matter, thermographic apparatus comprising a receptacle to contain thermographic powder, and means to move a said article along a path transversely of said receptacle and through thermographic powder therein, wherein said receptacle has a cross-section in said path of movement that is generally Nu -shaped and provided by first and second receptacle walls that extend upwardly away from the receptacle bottom and from a line of nearest mutual approach of said first and second receptacle walls, which line is at least adjacent said receptacle bottom, said walls forming an entrance slot at said line of nearest mutual approach, said second receptacle wall being concave with its upper surface providing, throughout its length, a support surface for a said article moving sequentially through the slot and through the receptacle, said first and second receptacle walls being mounted to extend away from one another as they extend upwardly away from said line of nearest approach, and an idler roll contained in the receptacle and resting on said surface and beneath which the article passes.
 7. Thermographic apparatus according to claim 6 comprising take-up means to move the workpiece with thermographic powder adhering thereto from the trough along a path, and heater means in said path having a plurality of individually energizable elongate heating elements spaced from one another transversely of said path and each directed longitudinally of said path.
 8. Apparatus according to claim 7, wherein said elongate heating elements are electrically energizable and are disposed parallel to one another substantially equispaced from one another transversely of said path.
 9. Apparatus according to claim 6 comprising a pre-entrance support for a said article; and wherein said entrance slot is defined by the lower edge of said first receptacle wall and the upper surface of said second receptacle wall, and said second receptacle wall projects past said entrance and exTernally of the receptacle to form said pre-entrance support and a restraint against loss of any powder leaking through said entrance. 